The invention relates to an electronic trip device for a multipole electrical circuit breaker protecting an electrical power system, comprising:
a current sensor per pole supplying a secondary current representative of a current flowing in an associated conductor of the power system protected by the circuit breaker, PA1 test current input means, PA1 a detection and rectifying circuit, to which the secondary currents and test current are applied, supplying signals representative of the currents flowing in the conductors to be protected and of the test current, PA1 an electronic processing unit receiving the signals supplied by the detection and rectifying circuit and delivering a tripping order, with or without a time delay, when the currents flowing in the conductors to be protected, an earth fault current or a test current exceed preset thresholds.
Test devices for electronic trip devices generally comprise a test socket equipped with terminals to which a test current is applied. This current simulates a fault current which could occur on secondary windings of the current transformers or sensors. According to the connection mode of the test socket terminals, the current is added or combines with the sensor currents in order to test the whole of the trip device. In state-of-the-art trip devices comprising protection functions called thermal or long delay, magnetic or short delay, and earth fault for earth protection, a discriminator enables the earth protection to be tested independently. When the test current is applied in a first direction, positive polarity on a first terminal and negative on a second, the trip device does not take account of this test current for earth protection and trips on long delay or short delay. If the current direction is inverted the trip device uses the test current to determine a value representative of the earth fault current and tripping is brought about by the earth protection. The means for determining the value representative of the earth fault current and the means for discriminating the test-current are, in state-of-the-art manner, integrated into the detection and rectifying circuit, as in French Patent FR-2,592,998, corresponding to the Patent EP-235,479.
In highly integrated electronic trip devices, the means for determining the value representative of the earth fault current are included in the processing unit, so as to reduce the cost and volume of the components. For the same reasons state-of-the-art type test current discrimination means can no longer be advantageously incorporated in the rectifying circuit.